1. Field of the Invention
The present invention relates to a miniature linear guide apparatus having a slider movable in the axial direction, and in particular, to an improved miniature linear guide apparatus which is very compact and light in weight and which facilitates interchanging sliders of a different width.
2. Description of the Prior Art
As a prior art miniature linear guide apparatus, there is a disclosure, for example, in Japanese Laid-Open Patent Publication No. 61-136018 (1986) and U.S. Pat. No. 4,647,226. In this prior art example, a table is placed on a bed having a U-shaped section so that the lower surface of the table faces the upper surface of a bottom wall of the bed. Each side wall of the bed is formed with a groove in the inner surface thereof in the longitudinal direction, and also, each lateral side of the table is formed with a groove in the longitudinal direction, so that the grooves of the table oppose the corresponding grooves of the bed. The corresponding grooves of the table and bed form a track channel, in which balls are assembled to constitute a bearing structure. A pair of no-load ball circulation paths are formed within the table in the longitudinal direction. This pair of no-load ball circulation paths are formed with an upper cover and a lower cover, that is, with a single member in the lateral direction and two members in the vertical direction. These upper and lower covers form a pair of no-load ball circulation paths which are fixed integrally to the table with rivets. In addition, on the opposed sides of the table, facing the inner surfaces of the side walls of the bed, there are provided additional retainers or protrusions for guiding the balls and maintaining the upper and lower covers in fixed relationship.
However, in the prior art miniature linear guide apparatus, since the retainers have protrusions arranged to guide the balls rolling along the track channels to the ball no-load circulation paths, the interval between the inner surface of the side wall of the bed and the side of the table cannot be reduced, resulting in shallow ball rolling grooves of the track channel. Consequently, the load capacity in the vertical direction is small, requiring the whole structure to become large and thus the weight of the table increases. This poses a problem in that the response is degraded and the frictional resistance is also increased.
Moreover, since the pair of no-load ball circulation paths formed within the table are formed with two upper and lower covers, and since these members and the retainers are fixed to the table integrally by means of rivets, the assembling is troublesome. Furthermore, when the upper cover and the lower cover are molded, if there is an error in molding, the upper and lower covers will deviate from each other after assembly. When such a deviation occurs, the rolling movement of the balls in the no-load ball circulation paths will be hindered, and the apparatus is defective resulting in low product yield.
Furthermore, since both no-load ball circulation paths are formed in a single member, in order to meet the requirement for a table of a different width, it is necessary to manufacture an upper cover and a lower cover anew which form the no-load ball circulation paths to match the design of the table of different width. This, in turn, requires manufacture of a new mold in order to manufacture the new members.